Cho Seung-Hui shared disturbing compositions in his writing classes, including a one-act play about a 13-year-old boy who tries to choke his stepfather with a cereal bar. He was a loner who rarely spoke, even to roommates, and who reportedly set a fire in a dorm room and stalked women.

But if such red flags are easy to spot, especially in hindsight, it's much harder to know at the time how to deal with them. And it's impossible to predict which individuals exhibiting such signs might pick up a gun and give violent expression to them, as Mr. Cho did Monday when he fatally shot 32 people before killing himself.

"If you wait until somebody wants to kill a lot of classmates, it's too late for counseling," notes Jack Levin, director of the Brudnick Center on Violence and Conflict at Northeastern University in Boston. "The problem is that those warning signs apply to far too many people. There are a lot of false positives."

Professor Levin suggests casting a broad net in terms of offering help and counseling services to such students. Others note that it's important to educate teachers, students, and administrators about the sorts of behavior they should look out for, as well as what to do when they see them.

In Cho's case, some classmates did in fact convey their concerns to administrators and police. Lucinda Roy, an English professor who taught Cho's poetry workshop, was so disturbed by his writing that she alerted campus police, counseling services, and other officials, The New York Times reported Wednesday. She also got permission to tutor Cho outside of class and was so concerned he might be dangerous that she set up a code with her assistant: If she said the name of a certain deceased professor, her assistant would call for help.

Noted US poet Nikki Giovanni told CNN that she had insisted Cho be removed from her class in 2005 because he had intimidated other students by photographing them and by writing obscene, violent poetry.

Ian McFarlane, a former classmate of Cho's, wrote in an AOL news blog that he was disturbed by Cho's writing but didn't know how to address it. "There isn't, to my knowledge, any system set up that lets people say, 'Hey! This guy has some issues! Maybe you should look into this guy!' "

Virginia Tech's shooting now has college counseling centers across the country reevaluating the measures they have in place to avert similar tragedies – and perhaps to provide the kind of system Mr. McFarlane says he wanted – even as they try to reassure students.

"It's really important to think, 'How would we manage if we have a student like this on our campus?' " says Joshua Miller, a Smith College professor who specializes in the psychology of trauma and crisis response. "How would we identify that person? If another student was concerned about them, how would we respond? What would be the various approaches that we could use in a way that's not overreacting and instilling fear in everybody?"

The signs to look for have, in fact, become fairly standard. While an FBI report on threat assessments for school shooters cautioned that there's no single profile of a shooter, it included many signs for fellow students and teachers to be alert to, including shared threats or violent fantasies, lack of empathy, low tolerance for frustration, and extreme alienation.

Even before Cho was identified as the shooter at Virginia Tech, many experts and psychologists detailed a general profile that he came to fit almost perfectly. Among other characteristics, mass school shooters tend to be men with psychological wounds from an abusive or troubled past. They are loners whose final outburst is often triggered by a rejection, real or perceived.

Investigators had trouble finding information about Cho because of his extreme social alienation. In both of his plays published online, adult male authority figures are described as having sexually molested or raped teenage boys. Accusations that Cho stalked women may indicate that he felt slighted by a woman.

Patient confidentiality laws make it hard for mental-health workers to speak out, even if they see troubling signs.

"There's an inherent conflict in that, for a dean of students to know which students are most at risk, they need as much information as possible," says Christopher Overtree, director of the Psychological Services Center at the University of Massachusetts, Amherst. "But for individual students to have their rights to medical- and mental-health privacy protected, that information needs to be kept from the deans. So you have this tricky loop."

A few schools have been trying innovative programs to get around that difficulty.

Cornell University in Ithaca, N.Y., decided to offer informal counseling sessions from an office in the engineering department – an option that led to a sharp increase in the number of students taking advantage of counseling, particularly those who had avoided more traditional psychological services. Cornell psychologists also began assisting students with practical concerns, such as visa issues.

"A lot of people at risk of suicide or even violence are people who are under an acute stressor, a family stress or some other kind of environmental or contextual stressor," says Greg Eells, the university's director of counseling and psychological services. "Sometimes it's really about those very practical advocacy things.… If a few key steps can be taken by somebody who knows the system, it gets the student out of that place of hopelessness."

Other universities have focused on educating students about the options available to them – the sort McFarlane says he wished he'd known about.

The University of California at Berkeley is in the midst of a three-year training effort to teach faculty and students how to confront a problem student and direct him or her to services. George Washington University's Hamilton Fish Institute on School and Community Violence has conducted training for resident advisers in dorms on how to deal with violent or potentially violent students.

Few challenge the importance of a communal effort, but some wonder if offering counseling is enough.

"There is a chance that a troubled person might go to a counselor instead of picking up a gun, but the history suggests that rage shooters are probably not going to," says Mike Males, senior researcher for the Center on Juvenile Criminal Justice in San Francisco.

The Chicago Tribune reported that Cho was taking antidepressants, which would indicate that he'd had some psychological treatment. "Even when they've been treated and medicated, they have still gone out and committed horrific crimes," adds Mr. Males.

Meanwhile, statistics show that the likelihood of such an incident recurring is negligible. From 2003 to 2005, the US Department of Education's Office of Postsecondary Education reported only 27 homicides out of a population of 14.4 million undergraduates at four-year colleges across the nation.